GDV1 C-terminal truncation of 39 amino acids disrupts sexual commitment in Plasmodium falciparum

Abstract

Malaria is a mosquito-borne disease caused by apicomplexan parasites of the genus Plasmodium. Completion of the parasites life cycle depends on the transmission of sexual stages, the gametocytes, from an infected human host to the mosquito vector. Sexual commitment occurs in only a small fraction of asexual blood stage parasites and is initiated by external cues. The gametocyte development protein 1 (GDV1) has been described as a key facilitator to trigger sexual commitment. GDV1 interacts with the silencing factor heterochromatin protein 1 (HP1), leading to its dissociation from heterochromatic DNA at the genomic locus encoding AP2-G, the master transcription factor of gametocytogenesis. How this process is regulated is not known. In this study we have addressed the role of protein kinases implicated in gametocyte development. From a pool of available protein kinase KO lines, we identified two kinase knockout lines which fail to produce gametocytes. However, independent genetic verification revealed that both kinases are not required for gametocytogenesis but both lines harbour the same mutation that leads to a truncation in the extreme C-terminus of GDV1. Introduction of the identified nonsense mutation into the genome of wild type parasite lines replicates the observed phenotype. Using a GDV1 overexpression line we show that the truncation in the GDV1 C-terminus does neither interfere with the nuclear import of GDV1 nor its interaction with HP1 in vitro, but appears important to sustain GDV1 protein levels and thereby sexual commitment. ImportanceTransmission of malaria causing Plasmodium species by mosquitos requires the parasite to change from a continuously growing asexual parasite form growing in the blood, to a sexually differentiated form, the gametocyte. Only a small subset of asexual parasites differentiates into gametocytes that are taken up by the mosquito. Transmission represents a bottleneck in the lifecycle of the parasite, so a molecular understanding of the events that lead to stage conversion may identify novel intervention points. Here we screened a subset of kinases we hypothesized to play a role in this process. While we did not identify kinases required for sexual conversion, we identified a mutation in the C-terminus of the Gametocyte Development 1 protein (GDV1), which abrogates sexual development. The mutation destabilises the protein but not its interaction with its cognate binding partner HP1. This suggest an important role for the GDV1 C-terminus beyond trafficking and protein stability.